This invention relates to heavy-load radial tires used for large vehicles such as trucks, buses and dump trucks.
In conventional heavy-load radial tires used for large vehicles such as trucks, buses and dump trucks, three or four belt layers of steel cords are laminated at an angle of 15 to 30 degress with respect to the tire circumference in the central part of the outside of a carcass-ply arranged perpendicular to the tire circumference. If a conventional radial tire is used for a long period of time, small cracks are formed at the cut end portions of the steel cords in the intermediate belt layer touching internally the outermost belt layer. The small cracks thus formed spread cooperating small cracks formed in the adjacent steel cords, so that the intermediate belt layer is separated from the tread crown part. This is caused by the fact that the end number of cords of the outermost belt layer is small and the cords are greatly spaced from one another, while the end number of cords of the intermediate cord layer is large similarly as in the end number of cords of the interior cord layer which is interior to the intermediate cord layer. This problem may be solved by decreasing the end number of cords of the intermediate belt layer and increasing the cord interval; however, the method suffers from the difficulties that the belt strength of the intermediate belt layer is decreased and accordingly the tire strength becomes insufficient.